The well-established solventborne, waterless coating compositions, especially those known as basecoat and clearcoat materials, and the single-coat or multicoat color and/or effect paint systems produced using them have very good performance properties.
However, the continually growing technical and aesthetic demands of the market, particularly the demands of the automobile manufacturers and their customers, require continual onward development of the technical and aesthetic level attained so far.
In particular there is a need to provide new coating compositions which even at low film thickness exhibit high hiding power and which at the same time are suitable for producing multicoat paint systems having good performance properties, especially good adhesive strength and good stonechip resistance. At the same time, however, the advantages acquired by virtue of the known basecoat and clearcoat materials and the multicoat paint systems produced from them are not to be lost, but instead are to be retained at least to the same extent and preferably to a greater extent.
Multicoat paint systems composed of basecoat and clearcoat are widespread in the automobile industry. Multicoat paint systems can be produced by first applying a basecoat material and, after a brief flash-off time, without a baking step (wet-on-wet method), applying a clearcoat material over the basecoat film, and then baking basecoat and clearcoat together. In the case of the innovative 3-wet coating methods, a basecoat is applied as a primer substitute; after a brief flash-off time, a further basecoat material is applied over it, and, after a further brief flash-off time, without a baking step (wet-on-wet-on-wet method), a clearcoat material is applied. Subsequently all three films (basecoat I+II and clearcoat) are baked jointly. Examples of 3-wet methods are described in WO 2006/062666 and in application EP 1940977.
Multicoat paint systems are used on account of their outstanding profiles of properties, such as scratch resistance, chemical resistance, and weather resistance, and also high gloss. For reasons of environmental protection, furthermore, there is a need to provide coating compositions having a lower and lower solvent content and hence a higher and higher solids content (high solids).
High-solids clearcoat materials which comply with the limits for volatile organic compounds (VOC) and which possess the high scratch resistance the customer demands are based predominantly on carbamate-containing binder systems, which in combination with monomeric crosslinking resins such as hexa(methoxymethyl)melamine (HMMM) or melamines with mixed etherification, and with polymerized binders, form a dense network. The volatile organic compounds (VOC) embrace the solvents and also volatile elimination products from film-forming reactions (cf. Römpp Lexikon Lacke and Druckfarben, Georg Thieme Verlag Stuttgart/New York 1998, ISBN 3-13-776001-1, page 612, entry heading “Volatile organic compounds” (VOC)).
The basecoat materials in the multicoat paint systems typically comprise a binder and a crosslinking agent. The binder frequently possesses hydroxy-functional groups on a polymeric network. Crosslinking agents used are typically monomeric crosslinking resins such as hexa(methoxymethyl)melamine (HMMM) or melamines with mixed etherification.
WO 2008/058590 A1 describes pigmented coating compositions comprising at least one inorganic particle (N) having a primary particle size of 1 to 800 nm, at least one binder (B), at least one color and/or effect pigment, and also one or more organic solvents, the inorganic particles (N) being at least partly modified with a stabilizer (S), which contains groups (S1), which are able to interact with the surface of the inorganic particles (N), and contains one or more hydrophobic substructures, the coating composition characteristically further comprising at least one wax or a waxlike compound (W). The document additionally describes the use of the pigmented coating compositions for producing multicoat paint systems, and also their use, and also a method of improving the flop of multicoat paint systems by using the pigmented coating compositions. Various binders (B) can be used. The paint systems obtained in this way have a particularly strongly pronounced light/dark behavior (metallic flop).
Nowadays, solventborne waterless high-solids basecoat materials are applied with a dry film thickness of around 16-20 μm, whereas, in the coating of waterborne basecoat materials, a film thickness of only 10-12 μm is customary. Reducing the basecoat film thickness to 10-12 μm can lead, in the case of solventborne basecoat materials, to a reduction in VOC emissions of 5 g per square meter of coated surface area.
However, reducing the dry film thickness of such basecoats frequently leads to a deterioration in the process stability, the hue stability, the substrate masking, and the further properties of the basecoat. In particular there are reductions in the hiding power of the coating film, the adhesive strength, and the stonechip resistance when the film thickness is reduced.
In order to improve the hiding power it is possible to raise the pigment content of the coating material. One measure of this is the pigment/binder ratio (p/b). The higher the p/b, the higher the pigment content of the basecoat formulation. Raising the pigment content, however, frequently leads to a further deterioration in the adhesive strength and the stonechip resistance of the coating.
Therefore it is necessary to develop high-solids waterless basecoat materials which even at low film thicknesses exhibit high hiding power in conjunction with good adhesive strength and stonechip resistance on the part of the coating, while exhibiting no other processing, application or technological problems and being suitable for automotive OEM finishing and also for automotive refinish.
The problem on which the present invention was based, therefore, was that of providing high-solids waterless basecoat materials from which coatings can be obtained that even at a low film thickness have a high hiding power in conjunction with high adhesive strength and high stonechip resistance.
It is particularly important to obtain a balanced tradeoff between adhesive strength and stonechip resistance on the one hand and good hiding power at low film thickness on the other hand.
In particular this ought also to be ensured for waterless basecoat materials having a relatively high solids content and pigment/binder ratio at spray viscosity.
Furthermore, the advantages achieved by means of the known high-solids basecoat and clearcoat materials, and the basecoats and clearcoats and multicoat paint systems produced from them, such as good flow, low bit count, and high consistency of hue, ought not to be lost but instead ought to be retained at least to the same extent and preferably to a greater extent.
The resulting paint systems ought in particular to exhibit very little haze, if any, and to have a very good overall visual appearance. Furthermore, the paint systems ought to be free from film defects such as mudcracking, clouds (areas of light/dark shading), and bits. Furthermore, the paint systems ought not to exhibit optical defects such as sanding marks, for example.
The intention was, further, to provide a process for preparing a waterless high-solids basecoat material that meets the above requirements.
Furthermore, the intention was to provide a multicoat paint system and also a process for producing it that exhibits the above advantages.
It was further intended that substrates of metal and/or plastic should be provided, coated with the multicoat paint system.